Reconstruction of blocks of video data using block size restriction

ABSTRACT

A method of decoding video data includes determining, by one or more processors implemented in circuitry, a partition of the video data into a plurality of blocks. The partition of the video data applies a block size restriction to prevent a splitting of a block of the plurality of blocks that would result in a small block comprising a block width and a block height when the block height times the block width is less than a threshold. The method further includes generating, by the one or more processors, prediction information for the block and determining, by the one or more processors, a predicted block for the block based on the prediction information. The method further includes decoding, by the one or more processors, a residual block for the block and combining, by the one or more processors, the predicted block and the residual block to decode the block.

This application claims the benefit of U.S. Provisional Application No.62/817,457, filed Mar. 12, 2019 and U.S. Provisional Application No.62/824,688, filed Mar. 27, 2019, each of which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for processing blocksof video data (e.g., small intra-coded blocks). In examples of thedisclosure, a video encoder may be configured to partition video datainto a plurality of blocks. For example, rather than processing a largeblock of 64×64 samples (e.g., pixels), the video encoder may split ablock into two or more smaller blocks, such as, for example, four 32×32blocks, sixteen 16×16 blocks, or other block sizes. In some examples,the video encoder may be configured to split blocks into relativelysmall sizes (e.g., 2×2 blocks, 2×4 blocks, 4×2 blocks, etc.). Similarly,a video decoder may be configured to determine a partition of the videodata into the plurality of blocks.

In accordance with example techniques of the disclosure, a video coder(e.g., a video encoder or a video decoder) may apply a block sizerestriction to prevent a split that leads to relatively small blocksizes. That is, during a partitioning of video data that splits largeblocks of video data into smaller blocks, the block size restriction mayprevent one or more splits that would lead to relatively small blocksizes. For example, the video coder may be configured to apply a blocksize restriction to prevent a splitting of a block that would result ina small block comprising a block width (in samples) and a block height(in samples) when the block height times the block width is less than athreshold number of samples (e.g., 16 samples). After partitioning thevideo data, the video coder may generate prediction information for theblock and determine a predicted block for the block based on thepredicted information. A predicted block may be dependent on neighboringblocks. For example, the video coder may determine a predicted block fora current block based on a top neighboring block and a left neighboringblock. By preventing splits that lead to relatively small block sizes,the video coder may determine the prediction information of blocks of aslice of video data with fewer block dependencies, thus potentiallydecreasing coding complexity with little to no loss in predictionaccuracy.

In one example, a method of decoding video data includes: determining,by one or more processors implemented in circuitry, a partition of thevideo data into a plurality of blocks, wherein the partition of thevideo data applies a block size restriction to prevent a splitting of ablock of the plurality of blocks that would result in a small blockcomprising a block width and a block height when the block height timesthe block width is less than a threshold; generating, by the one or moreprocessors, prediction information for the block; determining, by theone or more processors, a predicted block for the block based on theprediction information; decoding, by the one or more processors, aresidual block for the block; and combining, by the one or moreprocessors, the predicted block and the residual block to decode theblock.

In another example, a method of encoding video data includes:partitioning, by one or more processors implemented in circuitry, thevideo data into a plurality of blocks, wherein, to partition, the one ormore processors are configured to apply a block size restriction toprevent a splitting of a block of the plurality of blocks that wouldresult in a small block comprising a block width and a block height whenthe block height times the block width is less than a threshold;generating, by the one or more processors, prediction information forthe block; determining, by the one or more processors, a predicted blockfor the block based on the prediction information; generating, by theone or more processors, a residual block for the block based ondifferences between the block and the predicted block; and encoding, bythe one or more processors, the residual block.

In one example, a device for decoding video data includes a memoryconfigured to store video data and one or more processors implemented incircuitry and configured to: determine a partition of the video datainto a plurality of blocks, wherein the partition of the video dataapplies a block size restriction to prevent a splitting of a block ofthe plurality of blocks that would result in a small block comprising ablock width and a block height when the block height times the blockwidth is less than a threshold; generate prediction information for theblock; determine a predicted block for the block based on the predictioninformation; decode a residual block for the block; and combine thepredicted block and the residual block to decode the block.

In another example, a device for encoding video data includes a memoryconfigured to store video data and one or more processors implemented incircuitry and configured to: partition the video data into a pluralityof blocks, wherein the partitioning comprises applying a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width and a blockheight when the block height times the block width is less than athreshold; generate prediction information for the block; determine apredicted block for the block based on the prediction information;generate a residual block for the block based on differences between theblock and the predicted block; and encode the residual block.

In one example, a non-transitory computer-readable storage medium storesinstructions that, when executed, cause one or more processors of adevice to: determine a partition of the video data into a plurality ofblocks, wherein the partition of the video data applies a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width and a blockheight when the block height times the block width is less than athreshold; generate prediction information for the block; determine apredicted block for the block based on the prediction information;decode a residual block for the block; and combine the predicted blockand the residual block to decode the block.

In another example, a non-transitory computer-readable storage mediumstores instructions that, when executed, cause one or more processors ofa device to: partition the video data into a plurality of blocks,wherein the instructions that cause the one or more processors topartition cause the one or more processors to apply a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width and a blockheight when the block height times the block width is less than athreshold; generate prediction information for the block; determine apredicted block for the block based on the prediction information;generate a residual block for the block based on differences between theblock and the predicted block; and encode the residual block.

In one example, an apparatus configured to decode video data comprises:means for determining a partition of the video data into a plurality ofblocks, wherein the partition of the video data applies a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width and a blockheight when the block height times the block width is less than athreshold; means for generating prediction information for the block;means for determining a predicted block for the block based on theprediction information; means for decoding a residual block for theblock; and means for combining the predicted block and the residualblock to decode the block.

In another example, an apparatus configured to encode video datacomprises: means for partitioning the video data into a plurality ofblocks, wherein the means for partitioning comprises means for applyinga block size restriction to prevent a splitting of a block of theplurality of blocks that would result in a small block comprising ablock width and a block height when the block height times the blockwidth is less than a threshold; means for generating predictioninformation for the block; means for determining a predicted block forthe block based on the prediction information; means for generating aresidual block for the block based on differences between the block andthe predicted block; and means for encoding the residual block.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure and a corresponding coding tree unit (CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5A is a conceptual diagram illustrating an example of quad-treepartitioning.

FIG. 5B is a conceptual diagram illustrating an example of verticalbinary-tree partitioning.

FIG. 5C is a conceptual diagram illustrating an example of horizontalbinary-tree partitioning.

FIG. 5D is a conceptual diagram illustrating an example of verticalternary-tree partitioning.

FIG. 5E is a conceptual diagram illustrating an example of horizontalternary-tree partitioning.

FIG. 6 is a conceptual diagram illustrating an example of directions ofintra prediction.

FIG. 7 is a conceptual diagram illustrating an example of an 8×4rectangular block where closer reference samples are not used forprediction and farther reference samples may be used for prediction.

FIG. 8A is a conceptual diagram illustrating an example of a squareblock that does not use angular mode remapping.

FIG. 8B is a conceptual diagram illustrating an example of an angularmode remapping for a horizontal non-square block.

FIG. 8C is a conceptual diagram illustrating an example of angular moderemapping for a vertical non-square block.

FIG. 9 is a conceptual diagram illustrating an example of wide angles(−1 to −10, and 67 to 76) depicted in addition to a base set of 65angular modes.

FIG. 10 is a conceptual diagram illustrating an example of wide angles(−1 to −14, and 67 to 80) in versatile video coding test model 3 (VTM3)beyond modes 2 and 66 for a total of 93 angular modes.

FIG. 11 is a conceptual diagram illustrating an example of a referencesample array for intra-prediction of chroma components.

FIG. 12 is a conceptual diagram illustrating examples ofparallel-processable regions (PPRs) with a size of 64 samples (16 chromasamples).

FIG. 13 is a flowchart illustrating an example method for encoding acurrent block.

FIG. 14 is a flowchart illustrating an example method for decoding acurrent block of video data.

FIG. 15 is a flowchart illustrating an example method for encoding ablock using a block size restriction.

FIG. 16 is a flowchart illustrating an example method for decoding ablock using a block size restriction.

DETAILED DESCRIPTION

In general, this disclosure describes techniques for processing blocksof video data (e.g., intra-coded blocks). In examples of the disclosure,a video encoder may be configured to partition video data into aplurality of blocks. For example, rather than processing a large blockof 64×64 samples, the video encoder may split a block into two smallerblocks, such as, for example, four 32×32 blocks, sixteen 16×16 blocks,or other block sizes. In some examples, the video encoder may beconfigured to split blocks into relatively small sizes (e.g., 2×2blocks, 2×4 blocks, 4×2 blocks, etc.). For example, the video encodermay split a 16×8 block into two 8×8 blocks. Similarly, a video decodermay determine the partition of video data into the plurality of blocks.Rather than predicting the 16×8 block using motion informationrepresenting motion of all of the 128 samples (e.g., an average motionof the 128 samples), a video coder (e.g., video encoder or videodecoder) may predict a first 8×8 block using first motion informationrepresenting motion of 64 samples and predict a second 8×8 block usingsecond motion information representing motion of 64 samples, where thefirst motion information and the second motion information aredifferent. In this way, partitioning a relatively large block into two(or more) relatively small sizes may improve coding accuracy.

To reduce a complexity of coding with little or no loss in codingaccuracy, a video coder (e.g., a video encoder or video decoder) may beconfigured to represent a brightness of a block of video data using aluma component and color characteristics of the block of video datausing chroma components. The chroma components may include a blue minusluma value (‘Cb’) and/or a red minus luma value (‘Cr’). For example, avideo coder (e.g., a video encoder or video decoder) may be configuredto represent an 8×8 block by an 8×8 luma block (e.g., ‘Y’) of lumacomponents, a first 4×4 chroma block (e.g., ‘Cr’) of chroma componentsand a second 4×4 chroma block (e.g., ‘Cb’) of chroma components. Thatis, the chroma components of a block of video data may be subsampled tohave fewer samples than luma components of the block of video data. Inthis way, subsampling chroma components may improve a coding efficiencywith little or no loss of coding accuracy.

A video coder (e.g., a video encoder or video decoder) may be configuredto intra-code blocks where a predicted block is dependent on otherblocks. For example, the video coder may predict a current block using atop neighboring block and a left neighboring block to improve a codingaccuracy. As such, the video coder may not predict the current block inparallel with predicting the top neighboring block and a leftneighboring block. Instead, the video coder may wait to predict thecurrent block until completing a prediction of the top neighboring blockand the left neighboring block. The block dependency may increase acoding complexity that increases with smaller block sizes.

In accordance with the techniques of the disclosure, a video coder(e.g., a video encoder or video decoder) may apply a block sizerestriction to prevent a split that leads to relatively small blocksizes. As used herein, a split may refer to a partitioning of a blockinto smaller blocks. For example, the video coder may be configured toapply a block size restriction to prevent a splitting of a block thatwould result in a small block comprising a block width (in samples) anda block height (in samples) when the block height times the block widthis less than a threshold number of samples (e.g., 16 samples). The videocoder may apply the block size restriction to only chroma components ofa block. In another example, the video coder may apply the block sizerestriction to chroma components of a block and to luma components ofthe block. Applying the block restriction may help to reduce a codingcomplexity from block dependencies while having no or little impact oncoding accuracy.

After partitioning or splitting the video data, a video coder (e.g., avideo encoder or video decoder) may generate prediction information fora block and determine a predicted block for the block based on thepredicted information. Again, a predicted block may be dependent onneighboring blocks in the case of intra prediction. For example, thevideo coder may determine a predicted block for a current block based ona top neighboring block and a left neighboring block. By preventingsplits that lead to relatively small block sizes, the video coder maydetermine the prediction information of blocks of a slice of video datawith fewer block dependencies, thus potentially decreasing codingcomplexity with little to no loss in prediction accuracy.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.Techniques of this disclosure are generally directed to coding (encodingand/or decoding) video data. In general, video data includes any datafor processing a video. Thus, video data may include raw, uncoded video,encoded video, decoded (e.g., reconstructed) video, and video metadata,such as signaling data.

As shown in FIG. 1 , system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch smartphones, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, source device 102 and destination device 116 may be equippedfor wireless communication, and thus may be referred to as wirelesscommunication devices.

In the example of FIG. 1 , source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for processingsmall intra-coded blocks in parallel. Thus, source device 102 representsan example of a video encoding device, while destination device 116represents an example of a video decoding device. In other examples, asource device and a destination device may include other components orarrangements. For example, source device 102 may receive video data froman external video source, such as an external camera. Likewise,destination device 116 may interface with an external display device,rather than including an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forprocessing small intra-coded blocks in parallel. Source device 102 anddestination device 116 are merely examples of such coding devices inwhich source device 102 generates coded video data for transmission todestination device 116. This disclosure refers to a “coding” device as adevice that performs coding (encoding and/or decoding) of data. Thus,video encoder 200 and video decoder 300 represent examples of codingdevices, in particular, a video encoder and a video decoder,respectively. In some examples, devices 102, 116 may operate in asubstantially symmetrical manner such that each of devices 102, 116include video encoding and decoding components. Hence, system 100 maysupport one-way or two-way video transmission between video devices 102,116, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

In general, video source 104 represents a source of video data (i.e.,raw, uncoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some example, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally, oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may demodulate a transmission signalincluding the encoded video data, and input interface 122 may modulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, computer-readable medium 110 may include storagedevice 112. Source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, computer-readable medium 110 may include file server114 or another intermediate storage device that may store the encodedvideo data generated by source device 102. Source device 102 may outputencoded video data to file server 114 or another intermediate storagedevice that may store the encoded video generated by source device 102.Destination device 116 may access stored video data from file server 114via streaming or download. File server 114 may be any type of serverdevice capable of storing encoded video data and transmitting thatencoded video data to the destination device 116. File server 114 mayrepresent a web server (e.g., for a website), a file transfer protocol(FTP) server, a content delivery network device, or a network attachedstorage (NAS) device. Destination device 116 may access encoded videodata from file server 114 through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriberline (DSL), cable modem, etc.), or a combination of both that issuitable for accessing encoded video data stored on file server 114.File server 114 and input interface 122 may be configured to operateaccording to a streaming transmission protocol, a download transmissionprotocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receiver, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 1 , in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as ITU-T H.266, also referred toas Versatile Video Coding (VVC). A draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (Draft 8),” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 17^(th) Meeting: Brussels, BE, 7-17 Jan. 2020, JVET-Q2001-vA(hereinafter “VVC Draft 8”). The techniques of this disclosure, however,are not limited to any particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data (e.g., luma components and/or chromacomponents). In general, video encoder 200 and video decoder 300 maycode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is,rather than coding red, green, and blue (RGB) data for samples of apicture, video encoder 200 and video decoder 300 may code luminance andchrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) partitions. A triple tree partition is apartition where a block is split into three sub-blocks. In someexamples, a triple tree partition divides a block into three sub-blockswithout dividing the original block through the center. The partitioningtypes in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning a picture into CTUs, and partitioning of each CTU accordingto a corresponding partition structure, such as a QTBT structure, todefine CUs of the CTU. The syntax elements may further define predictionand residual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

To improve coding accuracy, a video coder (e.g., video encoder 200 orvideo decoder 300) may partition a block of data. For example, the videocoder may partition a block using a quad-tree split, a binary split, oranother split. The video coder may partition the block using a dualtree. For example, the video coder may partition chroma components ofthe block using a first tree (e.g., a chroma tree) and partition lumacomponents of the block using a second tree (e.g., a luma tree)different than the first tree. The video coder may partition the blockusing a single tree.

A video coder (e.g., video encoder 200 or video decoder 300) maydetermine a single tree for video data (e.g., a slice of video data)based on luma components for the block. For example, a block may berepresented by an 8×8 luma block (e.g., ‘Y’), a first 4×4 chroma block(e.g., ‘Cr’) and a second 4×4 chroma block (e.g., ‘Cb’). In thisexample, the video coder may generate the single tree to split the blocksuch that the 8×8 luma block is split into two 4×4 luma blocks. Thevideo coder may split the first 4×4 chroma block (e.g., ‘Cr’) into two2×2 chroma blocks and split the second 4×4 chroma block (e.g., ‘Cb’)into two 2×2 chroma blocks according to the single tree. In this way,the video coder may improve accuracy of a resulting predicted block forthe block, which may improve prediction accuracy of the video data.

However, when partitioning blocks of video data (e.g., intra-codedblocks), a video coder (e.g., video encoder 200 or video decoder 300)may split a block (e.g., chroma components of the block and/or lumacomponents of the block) into small blocks (e.g., a 2×2 block, a 2×4block, a 4×2 block, etc.). Moreover, each of the small blocks may have acoding dependency on neighboring blocks. For example, the video codermay determine a predicted block for each of the small blocks usingsamples of one or more neighboring blocks (e.g., a left neighbor blockand/or a top neighbor block). As such, the small blocks along with thedata dependencies may cause the video coder to sequentially determine apredicted block for each of the small blocks, which may result in highercoding complexity.

In accordance with example techniques of the disclosure, a video coder(e.g., video encoder 200 or video decoder 300) may be configured toapply a block size restriction to prevent a splitting of a block thatwould result in a small block. For example, the video coder may beconfigured to apply a block size restriction to prevent a splitting of ablock that would result in a small block comprising a block width and ablock height when the block height times the block width is less than athreshold number of samples (e.g., 4 samples, 16 samples, 32 samples, 64samples, etc.). For instance, a video coder (e.g., video encoder 200 orvideo decoder 300) may be configured to prevent splitting of an 4×4block, as such splitting would result in blocks that yield a product ofa block height times block width is less than 16 samples.

A video coder (e.g., video encoder 200 or video decoder 300) may beconfigured to split luma components for a block of video dataindependently from splitting chroma components for the block of videodata. For example, when preventing a splitting of a block (e.g., a 4×4block), the video coder may prevent a splitting of one or more chromablocks (e.g., 2×2 chroma blocks) for the block of video data and preventa splitting of a luma block (e.g., a 4×4 luma block) for the block ofvideo data. In some examples, however, the video coder may prevent asplitting of one or more chroma blocks (e.g., 2×2 chroma blocks) for theblock of video data and split a luma block (e.g., a 4×4 luma block) forthe block of video data when preventing a splitting of the 4×4 block. Inparticular, when the chroma blocks are subsampled relative to the lumablock, spitting the chroma blocks may result in a height by widthproduct that is less than a threshold number of samples but splittingthe luma block may result in a height by width product that is not lessthan the threshold number of samples.

A video coder (e.g., video encoder 200 or video decoder 300) may beconfigured to split luma components for a block of video data and tosplit luma components for the block of video data using a blockrestriction with different thresholds for luma and chroma. For example,the video coder may be configured to apply a block size restriction toprevent a splitting of chroma components for a block that would resultin a small chroma block comprising a block width and a block height whenthe block height times the block width is less than a first threshold.In this example, the video coder may be configured to apply the blocksize restriction to prevent a splitting of luma components for the blockthat would result in a small luma block comprising a block width and ablock height when the block height times the block width is less than asecond threshold that is different from the first threshold. In someexamples, however, the first threshold and the second threshold may bethe same.

A video coder (e.g., video encoder 200 or video decoder 300) may apply ablock size restriction to chroma components for a block of video dataindependently from luma components for the block of video data in asingle tree. For example, the video coder may determine a single treefor video data (e.g., a slice of video data) based on luma componentsfor the block. For instance, a block may be represented by an 8×8 lumablock (e.g., ‘Y’), a first 4×4 chroma block (e.g., ‘Cr’) and a second4×4 chroma block (e.g., ‘Cb’). In this example, the video coder maygenerate the single tree to split the block. In response to the singletree indicating a splitting of the block, the video coder may split theluma block (e.g., an 4×4 luma block) into smaller luma blocks (e.g., two2×4 luma blocks) according to the single tree. In response to the singletree indicating the splitting of the block, the video coder may apply ablock size restriction to prevent a splitting of the chroma blocks forthe block for video data. For instance, the video coder may refrain fromsplitting the first 2×2 chroma block (e.g., ‘Cr’) into two 2×1 chromablocks and a splitting of the second 2×2 chroma block (e.g., ‘Cb’) intotwo 2×1 chroma blocks.

After partitioning the video data, a video coder (e.g., video encoder200 or video decoder 300) may generate prediction information for ablock and determine a predicted block for the block based on thepredicted information. Again, a predicted block may be dependent onneighboring blocks. For example, the video coder may determine apredicted block for a current block based on a top neighboring block anda left neighboring block. By preventing block splits (e.g., chromacomponents and/or luma components) that lead to relatively small blocksizes, the video coder may determine the prediction information ofblocks of video data with fewer block dependencies, thus potentiallydecreasing coding complexity with little to no loss in predictionaccuracy.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagram illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, since quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level (i.e., a first level) ofQTBT structure 130 (i.e., the solid lines) and syntax elements (such assplitting information) for a prediction tree level (i.e., a secondlevel) of QTBT structure 130 (i.e., the dashed lines). Video encoder 200may encode, and video decoder 300 may decode, video data, such asprediction and transform data, for CUs represented by terminal leafnodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), they can be furtherpartitioned by respective binary trees. The binary tree splitting of onenode can be iterated until the nodes resulting from the split reach theminimum allowed binary tree leaf node size (MinBTSize) or the maximumallowed binary tree depth (MaxBTDepth). The example of QTBT structure130 represents such nodes as having dashed lines for branches. Thebinary tree leaf node is referred to as a coding unit (CU), which isused for prediction (e.g., intra-picture or inter-picture prediction)and transform, without any further partitioning. As discussed above, CUsmay also be referred to as “video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, it will not be further split by thebinary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in thisexample). Otherwise, the quadtree leaf node will be further partitionedby the binary tree. Therefore, the quadtree leaf node is also the rootnode for the binary tree and has the binary tree depth as 0. When thebinary tree depth reaches MaxBTDepth (4, in this example), no furthersplitting is permitted. When the binary tree node has width equal toMinBTSize (4, in this example), it implies that no further verticalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize implies that no further horizontal splitting ispermitted for that binary tree node. As noted above, leaf nodes of thebinary tree are referred to as CUs and are further processed accordingto prediction and transform without further partitioning.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 (VVC) video coding standard in development.However, the techniques of this disclosure are not limited to thesevideo coding standards, and are applicable generally to video encodingand decoding.

In the example of FIG. 3 , video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video encoder 200 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1 ). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1 ) may storethe object code of the software that video encoder 200 receives andexecutes, or another memory within video encoder 200 (not shown) maystore such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,uncoded version of the current block from video data memory 230 and theprediction block from mode selection unit 202. Residual generation unit204 calculates sample-by-sample differences between the current blockand the prediction block. The resulting sample-by-sample differencesdefine a residual block for the current block. In some examples,residual generation unit 204 may also determine differences betweensample values in the residual block to generate a residual block usingresidual differential pulse code modulation (RDPCM). In some examples,residual generation unit 204 may be formed using one or more subtractorcircuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar sizes for inter prediction. Videoencoder 200 and video decoder 300 may also support asymmetricpartitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for interprediction.

In examples where mode selection unit does not further partition a CUinto PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 120 may support CU sizes of 2N×2N, 2N×N, or N×2N.

Mode selection unit 202 may apply a block size restriction. For example,mode selection unit 202 may be configured to apply a block sizerestriction to prevent a splitting of a block that would result in asmall block comprising a block width and a block height when the blockheight times the block width is less than a threshold (e.g., 16samples). In some examples, mode selection unit 202 may apply the blocksize restriction to only chroma components of a block. That is, modeselection unit 202 may apply the block size restriction to chromacomponents of a block and refrain from applying the block sizerestriction to luma components of the block. In this way, mode selectionunit 202 may account for subsampling of the chroma components of ablock, which may reduce a coding complexity with little or no loss incoding accuracy. For instance, mode selection unit 202 may apply a blocksize restriction to prevent a split of chroma components of a blockpartition according to a single tree and split luma components of theblock. In some examples, mode selection unit 202 may apply the blocksize restriction to chroma components of a block and to luma componentsof the block. Applying the block restriction may help to reduce a codingcomplexity from block dependencies while having no or little impact oncoding accuracy.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying an MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding blocks andthe chroma coding blocks.

Video encoder 200 represents an example of an apparatus configured toencode video data including a memory (e.g., video data memory 230)configured to store video data, and one or more processors implementedin circuitry. Mode selection unit 202 may be configured to partition thevideo data into a plurality of blocks. To partition the video data, modeselection unit 202 may be configured to apply a block size restrictionto prevent a splitting of a block of the plurality of blocks that wouldresult in a small block comprising a block width and a block height whenthe block height times the block width is less than a threshold. Modeselection unit 202 may be configured to generate prediction informationfor the block resulting from the block size restriction. Mode selectionunit 202 may be configured to determine a predicted block for the blockbased on the prediction information. Residual generation unit 204 may beconfigured to generate a residual block for the block based ondifferences between the block and the predicted block. Entropy encodingunit 220 may encode the residual block.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of VVC and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 4 , video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video decoder 300 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1 ). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements and residual data)from an encoded video bitstream. Also, CPB memory 320 may store videodata other than syntax elements of a coded picture, such as temporarydata representing outputs from the various units of video decoder 300.DPB 314 generally stores decoded pictures, which video decoder 300 mayoutput and/or use as reference video data when decoding subsequent dataor pictures of the encoded video bitstream. CPB memory 320 and DPB 314may be formed by any of a variety of memory devices, such as dynamicrandom access memory (DRAM), including synchronous DRAM (SDRAM),magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types ofmemory devices. CPB memory 320 and DPB 314 may be provided by the samememory device or separate memory devices. In various examples, CPBmemory 320 may be on-chip with other components of video decoder 300, oroff-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1 ). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3 , fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, the one or more units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Prediction processing unit 304 may apply a block size restriction whensplitting blocks. For example, prediction processing unit 304 may beconfigured to apply a block size restriction to prevent a splitting of ablock that would result in a small block comprising a block width and ablock height when the block height times the block width is less than athreshold (e.g., 16 samples). Prediction processing unit 304 may applythe block size restriction to only chroma components of a block, whichmay reduce a coding complexity with little or no loss in codingaccuracy. That is, prediction processing unit 304 may apply the blocksize restriction to chroma components of a block and refrain fromapplying the block size restriction to luma components of the block. Inthis way, prediction processing unit 304 may account for subsampling ofthe chroma components of a block. For instance, prediction processingunit 304 may apply a block size restriction to prevent a split of chromacomponents of a block partition according to a single tree and splitluma components of the block. In another example, prediction processingunit 304 may apply the block size restriction to chroma components of ablock and to luma components of the block. Applying the blockrestriction may help to reduce a coding complexity from blockdependencies while having no or little impact on coding accuracy.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3 ).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3 ).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures fromDPB for subsequent presentation on a display device, such as displaydevice 118 of FIG. 1 .

In this manner, video decoder 300 represents an example of an apparatusincluding a memory (e.g., video data memory 230) configured to storevideo data, and one or more processing units implemented in circuitryand configured to determine a plurality of intra-coded blocks forgenerating prediction information. Prediction processing unit 304 may beconfigured to determine a partition of the video data into a pluralityof blocks, where the partition of the video data may apply a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width (in samples)and a block height (in samples) when the block height times the blockwidth is less than a threshold number of samples. Prediction processingunit 304 may be configured to generate prediction information for theblock. Prediction processing unit 304 may be configured to determine apredicted block for the block based on the prediction information.Entropy decoding unit 302 may be configured to decode a residual blockfor the block. Reconstruction unit 310 may be configured to combine thepredicted block and the residual block to decode the block.

FIGS. 5A-5E illustrate examples of four splitting types in multi-typetree structure. In HEVC, a CTU is split into CUs by using aquaternary-tree structure denoted as coding tree to adapt to variouslocal characteristics. The decision of whether to code a picture areausing inter-picture (temporal) or intra-picture (spatial) prediction ismade at the leaf CU level. Each leaf CU can be further split into one,two, or four PUs according to the PU splitting type. Inside one PU, thesame prediction process is applied, and the relevant information istransmitted to the decoder on a PU basis. After obtaining the residualblock by applying the prediction process based on the PU splitting type,a leaf CU can be partitioned into transform units (TUs) according toanother quaternary-tree structure like the coding tree for the CU. Afeature of the HEVC structure is that the HEVC structure has multiplepartition concepts including CU, PU, and TU.

In VVC, a quadtree with nested multi-type tree using binary and ternarysplits segmentation structure replaces the concepts of multiplepartition unit types. That is, VVC removes the separation of the CU, PUand TU concepts of HEVC except as needed for CUs that have a size toolarge for the maximum transform length. As such, VVC may support moreflexibility for CU partition shapes than HEVC. In the coding treestructure, a CU can have either a square or rectangular shape. A videocoder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) first partitions a coding treeunit (CTU) by a quaternary tree (a.k.a. quadtree) structure. Then, thevideo coder further partitions the quaternary tree leaf nodes by amulti-type tree structure.

FIG. 5A is a conceptual diagram illustrating an example of quad-treepartitioning including a vertical binary split 440 (“SPLIT_BT_VER”) anda horizontal binary split 441 (“SPLIT_BT_HOR”). FIG. 5B is a conceptualdiagram illustrating an example of vertical binary-tree partitioningincluding a vertical binary split 442. FIG. 5C is a conceptual diagramillustrating an example of horizontal binary-tree partitioning includinga horizontal binary split 443. FIG. 5D is a conceptual diagramillustrating an example of vertical ternary-tree partitioning includingvertical ternary splits 444, 445 (“SPLIT_TT_VER”). FIG. 5E is aconceptual diagram illustrating an example of horizontal ternary-treepartitioning including horizontal ternary splits 446, 447(“SPLIT_TT_HOR”). The multi-type tree leaf nodes are called coding units(CUs), and unless the CU is too large for the maximum transform length,a video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may use this segmentation forprediction and transform processing without any further partitioning.This means that, in most cases, the CU, PU and TU may have the sameblock size in the quadtree with nested multi-type tree coding blockstructure. The exception may occur when a maximum supported transformlength is smaller than a width or height of a colour component of theCU.

In VVC, a CTU consists of a luma coding tree block (CTB) and two chromacoding tree blocks. At the CU level, a CU is associated with a lumacoding block (CB) and two chroma coding blocks. As in VTM (the referencesoftware of the VVC), the luma tree and the chroma tree are separated inintra slices (referred to as dual tree structure) while they are sharedin inter slices (referred to as single tree or shared tree structure).The size of a CTU can be up to 128×128 (luma component) while the sizeof a coding unit may range from 4×4 to the size of CTU. In thisscenario, the size of a chroma block can be 2×2, 2×4, or 4×2 in 4:2:0color format. While examples described herein are directed to the 4:2:0color format, which subsamples to half the resolution along a verticaldirection and to half the resolution along a horizontal direction, othercolor formats (e.g., the 4:2:2 color format) may be used.

FIG. 6 is a conceptual diagram illustrating directions of intraprediction, arrows points towards the reference samples. For the lumacomponent, intra prediction involves DC, planar, and directional (orangular) prediction mode. Directional prediction for square blocks usesdirections between −135 degrees to 45 degrees of the current block inthe VVC test model 2 (VTM2), as depicted in FIG. 6 .

In VTM2, a block structure used for specifying the prediction block forintra prediction is not restricted to be square (width w=height h).Rectangular or non-square prediction blocks (w>h or w<h) can increasethe coding efficiency based on the characteristics of the content.

In such rectangular blocks, restricting a direction of intra predictionto be within −135 degrees to 45 degrees can result in situations wherefarther reference samples are used rather than closer reference samplesfor intra prediction. Such a design is likely to have an impact on thecoding efficiency; it is more beneficial to have the range ofrestrictions relaxed so that closer reference samples (e.g., samplesbeyond the −135 to 45-degree angle) can be used for prediction. Anexample of such a case is given in FIG. 7 .

FIG. 7 is a conceptual diagram illustrating an 8×4 rectangular block 500where “closer” reference samples 502 (dashed arrows) are not used, butfarther reference samples 504 (dashed circle) may be used, due torestriction of intra prediction direction to be in the range −135degrees to 45 degrees. During the 12^(th) JVET meeting, a modificationof wide-angle intra prediction was adopted into VTM3. This adoptionincludes two modifications to unify the angular intra prediction forsquare and non-square blocks. Firstly, angular prediction directions aremodified to cover diagonal directions of all block shapes. Secondly, allangular directions are kept within the range between the bottom-leftdiagonal direction and the top-right diagonal direction for all blockaspect ratios (square and non-square) as illustrated in FIGS. 8A-8C. Inaddition, the number of reference samples in the top reference row andleft reference column are restricted to 2*width+1 and 2*height+1 for allblock shapes. An illustration of wider angles that are adopted in VTM3is provided in FIG. 10 . Although VTM3 defines 95 modes, for any blocksize only 67 modes are allowed. The exact modes that are allowed dependon the ratio of block width to height. This is done by restricting themode range for certain block sizes.

FIGS. 8A-8C are conceptual diagrams illustrating an example of a modemapping process for modes outside the diagonal direction range.Specifically, FIG. 8A is a conceptual diagram illustrating an example ofa square block 602 with diagonal direction 604 and diagonal direction606, which does not require angular mode remapping. FIG. 8B is aconceptual diagram illustrating an example of angular mode remapping forhorizontal non-square block 612 with diagonal direction 614 and diagonaldirection 616. FIG. 8C is a conceptual diagram illustrating an exampleof angular mode remapping for vertical non-square block 622 withdiagonal direction 624 and diagonal direction 626.

Table 1 specifies a mapping table between predModeIntra and the angleparameter intraPredAngle in VTM3. Some of the angular modes correspondwith non-square block diagonals. In the following, angular modes with apositive intraPredAngle value are referred to as positive angular modes(mode index<18 or >50), while angular modes with a negativeintraPredAngle value are referred to as negative angular modes (modeindex>18 and <50).

TABLE 1 Specification of intraPredAngle predModeIntra −14 −13 −12 −11intraPredAngle 512 341 256 171 predModeIntra −10 −9 −8 −7 −6 −5 −4 −3 −2−1 2 3 4 5 6 7 8 intraPredAngle 128 102 86 73 64 57 51 45 39 35 32 29 2623 20 18 16 predModeIntra 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 2425 intraPredAngle 14 12 10 8 6 4 3 2 1 0 −1 −2 −3 −4 −6 −8 −10predModeIntra 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42intraPredAngle −12 −14 −16 −18 −20 −23 −26 −29 −32 −29 −26 −23 −20 −18−16 −14 −12 predModeIntra 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5758 59 intraPredAngle −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6 8 10 12 14predModeIntra 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76intraPredAngle 16 18 20 23 26 29 32 35 39 45 51 57 64 73 86 102 128predModeIntra 77 78 79 80 intraPredAngle 171 256 341 512

FIG. 9 is a conceptual diagram illustrating an example of wide angles(−1 to −10, and 67 to 76) depicted in addition to the 65 angular modes.FIG. 10 is a conceptual diagram illustrating an example of wide angles(−1 to −14, and 67 to 80) in VTM3 beyond modes 2 and 66 for a total of93 angular modes.

Some designs of VVC support eight intra prediction modes for the chromacomponent, including PLANAR, vertical “VER”, horizontal “HOR”, DC, LM,multi-directional linear model ‘L’ (MDLM_L), MDLM_T, and derived mode(DM). In order to encode a chroma intra coded CU, a video encoder (e.g.,video encoder 200) may use a flag to indicate whether this CU is DMcoded or not. If the CU is decided to be DM coded, a video decoder(e.g., video decoder 300) may use the intra prediction mode of thecorresponding luma component to get the prediction for this CU.Otherwise, the video encoder may signal the mode of the CU to thedecoder. A video coder (e.g., video encoder 200 or video decoder 300)may reconstruct samples of the top neighboring block in the VER mode andmay reconstruct samples of the left neighboring block in the HOR mode topredict the current block. The video coder may reconstruct samples ofboth the top and left neighboring blocks in the PLANAR and DC mode forprediction. The video coder may reconstruct samples of the correspondingluma blocks that are used for the prediction for the LM, MDLM_L, andMDLM_T modes.

FIG. 11 is a conceptual diagram illustrating reference sample array forintra-prediction of chroma components. A video coder (e.g., videoencoder 200 or video decoder 300, or in some examples, mode selectionunit 202 of video encoder 200 or prediction processing unit 304 of videodecoder 300) may use the samples in a neighbourhood of a coding block640 for intra prediction of the block. Typically, the video coder usesthe reconstructed reference sample lines that are closest to the leftand the top boundaries of coding block 640 as the reference samples forintra prediction. For example, the video coder may use reconstructionsamples of a top line 642 and/or a left line 644. However, VVC alsoenables other samples in the neighbourhood of coding block 640 to beused as reference samples (e.g., top-left, left-below, top-right). Forexample, the video coder may use reconstruction samples of a top-leftpixel 648, a left-below line 650, and/or a top-right line 646.

In VVC, a video coder (e.g., video encoder 200 or video decoder 300, orin some examples, mode selection unit 202 of video encoder 200 orprediction processing unit 304 of video decoder 300) may use onlyreference lines with MRLIdx equal to 0, 1 and 3 for the luma component.FIG. 11 illustrates MRLIdx equal to 0. In VVC, the video coder maypredict the cross-component linear model (CCLM) chroma block from theluma reconstructed sample. In this example, for other chroma intrablocks, the video coder may predict the prediction from only the linewith MRLIdx=0. For the luma, the video coder may predict the predictionusing a MRLIdx of 0, 1, 2 (previously 0, 1 and 3, but in WD8, the MRLIdxis modified to be 0, 1, and 2). A video encoder (e.g., video encoder 200may signal the MRLIdx in a bitstream.

For the chroma component, the video coder may use only the referenceline with MRLIdx equal to 0 as depicted in FIG. 11 . The video coder maycode the index to the reference line used for coding the block (values0, 1 and 2 indicating lines with MRLIdx 0, 1 and 3, respectively) with atruncated unary codeword. The video coder may not use planar and DCmodes for the reference line with MRLIdx>0. In some examples, the videocoder may add only the available samples of the neighbourhood of acoding block to the reference array for intra-prediction. Availabilitychecking of the samples in VVC is presented in the following.

8.4.4.2.2 Reference Sample Availability Marking Process

Inputs to this process are:

a sample location (xTbCmp, yTbCmp) specifying the top-left sample of thecurrent transform block relative to the top left sample of the currentpicture,

a variable refIdx specifying the intra prediction reference line index,

a variable refW specifying the reference samples width,

a variable refH specifying the reference samples height,

a variable cIdx specifying the colour component of the current block.

Outputs of this process are the reference samples refUnfilt[x][y] withx=−1−refIdx, y=−1−refIdx . . . refH−1 and x=−refIdx . . . refW−1,y=−1−refIdx for intra sample prediction.

The refW+refH+1+(2*refIdx) neighbouring samples refUnfilt[x][y] that areconstructed samples prior to the in-loop filter process, withx=−1−refIdx, y=−1−refIdx . . . refH−1 and x=−refIdx . . . refW−1,y=−1−refIdx, are derived as follows:

The neighbouring location (xNbCmp, yNbCmp) is specified by:(xNbCmp,yNbCmp)=(xTbCmp+x,yTbCmp+y)   (8-108)

The current luma location (xTbY, yTbY) and the neighbouring lumalocation (xNbY, yNbY) are derived as follows:(xTbY,yTbY)=(cIdx==0)?(xTbCmp,yTbCmp):(xTbCmp<<1,yTbCmp<<1)  (8-109)(xNbY,yNbY)=(cIdx==0)?(xNbCmp,yNbCmp):(xNbCmp<<1,yNbCmp<<1)  (8-110)

The availability derivation process for a block as specified in clause6.4.X

-   -   [Ed. (BB): Neighbouring blocks availability checking process        tbd] is invoked with the current luma location (xCurr, yCurr)        set equal to (xTbY, yTbY) and the neighbouring luma location        (xNbY, yNbY) as inputs, and the output is assigned to        availableN.        -   Each sample refUnfilt[x][y] is derived as follows:        -   If availableN is equal to FALSE, the sample refUnfilt[x][y]            is marked as “not available for intra prediction”.

Otherwise, the sample refUnfilt[x][y] is marked as “available for intraprediction” and the sample at the location (xNbCmp, yNbCmp) is assignedto refUnfilt[x][y].

When the reference sample availability marking is finished, a videocoder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may obtain the unavailablesample using a reference sample substitution process as presented in thefollowing.

8.4.4.2.3 Reference Sample Substitution Process

Inputs to this process are:

-   -   a variable refIdx specifying the intra prediction reference line        index,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   reference samples refUnfilt[x][y] with x=−1−refIdx, y=−1−refIdx        . . . refH−1 and x=−refIdx . . . refW−1, y=−1−refIdx for intra        sample prediction,    -   a variable cIdx specifying the colour component of the current        block.

Outputs of this process are the modified reference samplesrefUnfilt[x][y] with x=−1−refIdx, y=−1−refIdx . . . refH−1 and x=−refIdx. . . refW−1, y=−1−refIdx for intra sample prediction.

The variable bitDepth is derived as follows:

-   -   If cIdx is equal to 0, bitDepth is set equal to BitDepthY    -   Otherwise, bitDepth is set equal to BitDepthC.

The values of the samples refUnfilt[x][y] with x=−1−refIdx, y=−1−refIdx. . . refH−1 and x=−refIdx . . . refW−1, y=−1−refIdx are modified asfollows:

-   -   If all samples refUnfilt[x][y] with x=−1−refIdx, y=−1−refIdx . .        . refH−1 and x=−refIdx . . . refW−1, y=−1−refIdx are marked as        “not available for intra prediction”, all values of        refUnfilt[x][y] are set equal to 1<<(bitDepth−1    -   Otherwise (at least one but not all samples refUnfilt[x][y] are        marked as “not available for intra prediction”), the following        ordered steps apply:

1. When refUnfilt[−1−refIdx][refH−1] is marked as “not available forintra prediction”, search sequentially starting from x=−1−refIdx,y=refH−1 to x=−1−refIdx, y=−1−refIdx, then from x=−refIdx, y=−1−refIdxto x=refW−1, y=−1−refIdx, for a sample refUnfilt[x][y] that is marked as“available for intra prediction”. Once a sample refUnfilt[x][y] markedas “available for intra prediction” is found, the search is terminatedand the value of refUnfilt[−1−refIdx][refH−1] is set equal to the valueof refUnfilt[x][y].

2. For x=−1−refIdx, y=refH−2 . . . −1−refIdx, when refUnfilt[x][y] ismarked as “not available for intra prediction”, the value ofrefUnfilt[x][y] is set equal to the value of refUnfilt[x][y+1].

3. For x=0 . . . refW−1, y=−1, when refUnfilt[x][y] is marked as “notavailable for intra prediction”, the value of refUnfilt[x][y] is setequal to the value of refUnfilt[x−1][y].

All samples refUnfilt[x][y] with x=−1−refIdx, y=−1−refIdx . . . refH−1and x=−refIdx . . . refW−1, y=−1−refIdx are marked as “available forintra prediction”.

In order to increase the processing throughput of intra coding, sometechniques disable small block sizes, e.g., 2×2, 2×4, and 4×2 in dualtree. For a single tree, some systems may share reference samples forsmall blocks. When sharing reference samples for small blocks, parallelregions including several small blocks may be defined in which all thesub-blocks in the region can be processed in parallel. Although thistechnique can increase the worst-case processing throughput, thistechnique makes the prediction more complicated. The reason is that asignificant change of intra prediction may be needed to decide thereference samples because the prediction may not use samples ofneighbouring blocks as reference.

In some hardware video encoders and video decoders, processingthroughput is reduced when a picture has more small blocks. Suchprocessing throughput drop may come from small intra blocks or intrablock copy (IBC) blocks. A reason that the throughput drop comes fromsmall intra blocks or IBC blocks is intra blocks have data dependencybetween neighbouring blocks (e.g., the predictor generation of an intrablock requires top and left boundary reconstructed samples fromneighbouring blocks) and must be processed sequentially. In addition,the small IBC blocks may use reconstructed samples of the spatialneighbouring blocks for prediction that may lead to predictiondependency.

In HEVC, the worst-case processing throughput may occur when 4×4 chromaintra blocks are processed. In the VVC test model 4.0 (VTM 4.0), thesize of the smallest intra block is 2×2, and the reconstruction processof a chroma intra block becomes very complex due to the adoption of newtools, such as, for example, but not limited to, cross-component linearmodel (CCLM) techniques, position dependent prediction combination(PDPC) techniques, references smoothing techniques, or other new tools.

Techniques described herein may include configuring video encoder 200and/or video decoder 300 to enable processing of small intra-codedblocks and/or IBC blocks in parallel and thus increase the processingthroughput of video encoder 200 and/or video decoder 300.

Techniques described herein may include configuring a video coder (e.g.,video encoder 200 or video decoder 300, or in some examples, modeselection unit 202 of video encoder 200 or prediction processing unit304 of video decoder 300) to include block size restriction and removedependency between neighbouring blocks.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to not allow(e.g., prevent) a split that leads to small blocks (e.g.,blkWidth*blkHeight<Threshold). Said differently, a video encoder (e.g.,video encoder 200 or in some examples, mode selection unit 202 of videoencoder 200) may be configured to partition video data into a pluralityof blocks, where the partitioning comprises applying a block sizerestriction to prevent a splitting of a block of the plurality of blocksthat would result in a small block comprising a block width and a blockheight when the block height times the block width is less than athreshold. A video decoder (e.g., video decoder 300 or in some examples,prediction processing unit 304 of video decoder 300) may be configuredto determine a partition of video data into a plurality of blocks, wherethe partition applies a block size restriction to prevent a splitting ofa block of the plurality of blocks that would result in a small blockcomprising a block width and a block height when the block height timesthe block width is less than a threshold. In some example, the thresholdmay be set to 16. As such, the video coder may be configured to restrictthe blocks sizes 2×2, 2×4 and 4×2, e.g., to prevent splitting of blocksinto blocks sizes 2×2, 2×4 and 4×2. In this example, the video coder maybe configured to not allow quadtree-split (QT) and binary split (BT) foran 4×4 block, and triple split is restricted for 8×2 or 2×8 blocks.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to apply theblock size restriction for only chroma components in dual tree. Saiddifferently, a video encoder (e.g., video encoder 200, or in someexamples, mode selection unit 202 of video encoder 200) may partitionluma components for a block according to a luma tree of a dual tree andchroma components for the block according to a chroma tree of the dualtree. In this example, the video encoder may apply the block sizerestriction to only the chroma components for the block. A video decoder(e.g., video decoder 300, or in some examples, prediction processingunit 304 of video decoder 300) may determine a partition of lumacomponents for a block according to a luma tree of a dual tree andchroma components for the block according to a chroma tree of the dualtree. In this example, the partition may apply the block sizerestriction to only the chroma components for the block.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to apply theblock size restriction for both chroma components and the luma componentin dual tree. Said differently, a video encoder (e.g., video encoder200, or in some examples, mode selection unit 202 of video encoder 200)may partition luma components for a block according to a luma tree of adual tree and chroma components for the block according to a chroma treeof the dual tree. In this example, the video encoder may apply the blocksize restriction to the chroma components for the block and the lumacomponents for the block. A video decoder (e.g., video decoder 300, orin some examples, prediction processing unit 304 of video decoder 300)may determine a partition of luma components for a block according to aluma tree of a dual tree and chroma components for the block accordingto a chroma tree of the dual tree. In this example, the partition mayapply the block size restriction to the chroma components for the blockand the luma components for the block.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to apply theblock size restriction for only the chroma component in single tree. Forinstance, the video coder may refrain from comparing a resulting lumablock for the block to a threshold. In this example, the video coder maybe configured to apply dependency removal techniques for removingdependency between neighbouring blocks of this disclosure to the chromasmall block sizes.

In some examples of single tree, a split of a chroma block may beindependent from a split of a luma block when this split results insmall blocks which have blkWidth*blkHeight<Threshold. For example, withthreshold of 16, if an 8×8/4×16/16×4 luma block is split further, thevideo coder may be configured to not split the corresponding chromablock. Said differently, a video encoder (e.g., video encoder 200, or insome examples, mode selection unit 202 of video encoder 200) may beconfigured to partition luma components for a block and chromacomponents for the block according to a single tree. In this example, topartition, the video encoder may split the luma components for the blockand apply the block size restriction to prevent a splitting of thechroma components for the block. A video decoder (e.g., video decoder300, or in some examples, prediction processing unit 304 of videodecoder 300) may be configured to determine a partition of lumacomponents for a block and chroma components for the block according toa single tree that splits the luma components for the block. In thisexample, the partition of the video data applies the block sizerestriction to prevent a splitting of the chroma components for theblock. The luma components may form, for example, an 8×8 luma block, a4×16 luma block, or a 16×4 luma block. Said differently, the lumacomponents may form an 8×8 luma block, a 4×16 luma block, or a 16×4 lumablock before splitting the luma components for the block. That is, whenthe luma components form an 8×8 luma block, a 4×16 luma block, or a 16×4luma block before splitting the luma components for the block, thechroma block may be less than a threshold of 16 due to sub-sampled sizeof the chroma components (e.g., 4:2:0) while the luma block remainsgreater than or equal to the threshold of 16.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to remove adependency between neighbouring blocks. For example, the video coder maybe configured to define a parallel-processable region (PPR). The videocoder may be able to process all the blocks covered by the PPR region inparallel. The video coder may be configured to set the minimum number ofsamples in a PPR by a threshold or a value signalled in the bitstream.

For example, if the threshold is 64, the shape of theparallel-processable region may be as in FIG. 12 . FIG. 12 is aconceptual diagram illustrating examples of PPRs with the size of 64samples (16 chroma samples). A video coder (e.g., video encoder 200 orvideo decoder 300, or in some examples, mode selection unit 202 of videoencoder 200 or prediction processing unit 304 of video decoder 300) maybe configured to define the root sample (R) of a PPR as the top-leftsample of the top-left block of the region. The video coder may beconfigured to define the distance of the n^(th) block to the root as(dX_(n), dY_(n))=(X_(n)−X_(R), Y_(n)−Y_(R)), where (X_(n), Y_(n)) and(X_(R), Y_(R)) are the positions of the top-left sample of the n^(th)block and the root sample, respectively. dXn, dYn may represent adistance of the top-left sample of block nth to the top-left sample of aPPR (e.g., root) along a horizontal direction and along a verticaldirection, respectively.

A PPR may be of rectangular shape; however, in some cases, a video coder(e.g., video encoder 200 or video decoder 300, or in some examples, modeselection unit 202 of video encoder 200 or prediction processing unit304 of video decoder 300) may be configured to define a PPR as a unionof rectangular shapes; the rectangular shapes constituting the PPR mayor may not be adjacent.

In FIG. 12 , two examples of PPR with non-adjacent rectangular blocks isshown. For a 4×8 block with a vertical triple split, two non-adjacent4×2 blocks are generated and they form a PPR of 16 samples; the 4×4block is not considered to part of the PPR. That is, the first exampleincludes a 4×8 block 670 and the second example includes an 8×4 block672.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to performmode restriction. To remove a dependency between neighbouring blocks ina region, the video coder may be configured to limit the prediction modecandidate list of a block based on a position of the block in theparallel region.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to remove aprediction mode that uses the samples from the neighbour blocks of thesame PPR from the candidate list. For example, for a block that hasnon-zero dXn, the video coder may be configured to restrict a DCprediction, a planar (PL) mode prediction, and/or a horizontal (HOR)mode prediction. The video coder may be configured to disallow derivedmode (DM) if the mode of the corresponding luma area is a DC mode, a PLmode, or a HOR mode. The position-dependent prediction combination(PDPC) process may not use the samples of the left neighbouring block.

For a block that has non-zero dYn, a video coder (e.g., video encoder200 or video decoder 300, or in some examples, mode selection unit 202of video encoder 200 or prediction processing unit 304 of video decoder300) may be configured to disallow a DC prediction, a PL prediction,and/or a VER prediction. The video coder may be configured to disable aDM mode if the mode of the corresponding luma area is a DC mode, a PLmode, or a vertical (VER) mode. The PDPC process may not use the samplesof the above neighbouring block.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to allowonly a DC prediction for a block which has at least one of dXn and dYnbeing non-zero. In this case, the video coder may be configured to notuse the samples located within the PPR to calculate the DC value. Whenboth dXn and dYn are non-zero, the video coder may be configured to usethe DC mode where the DC value is set equal to a predefined value.

In case a parallel-processable region includes two separated blocks, avideo coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to processthe blocks in the PPR before the intermediate blocks that do not belongto the region. In this case, the video coder may be configured torestrict a prediction that uses the reference samples from theintermediate block.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to disableIBC mode for small blocks (e.g., 2×2, 2×4, 4×2).

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to disableIBC mode for all small blocks (e.g., 2×2, 2×4, 4×2) excluding the firstblock in the PPR (the top-left block in the PPR).

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to excludeall the blocks in a PPR from the IBC prediction area of other blocks inthe same PPR.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to set theprediction samples for small IBC blocks in PPR equal to a default value.The video coder may be configured to determine the default value basedon the bit-depth being used to present the samples.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to clip themotion vector of small chroma blocks in PPR such that the referenceblock does not overlap the PPR.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to removeone or more samples from a reference samples array that makeneighbouring blocks dependent. For example, the video coder may beconfigured to mark a block in a PPR as “unavailable” for intraprediction of other blocks within the same PPR. For instance, the videocoder may be configured to not use the samples of the block within theparallel-processable region for others blocks in the same PPR. In thiscase, the video coder may be configured to substitute a prediction thatrefers to unavailable samples by a value.

The availability of neighbour block checking for intra prediction of ablock may be based on the block's position in the PPR. If a block hasnon-zero dXn, a video coder (e.g., video encoder 200 or video decoder300, or in some examples, mode selection unit 202 of video encoder 200or prediction processing unit 304 of video decoder 300) may beconfigured to mark the left and the left-below blocks as unavailable. Ifa block has non-zero dYn, the video coder may be configured to mark thetop and top-right blocks as unavailable. If both dXn and dYn of a blockare non-zero, the video coder may be configured to mark the left-below,left, top-left, top, and top-right blocks as unavailable. Again, aprediction that refers to unavailable samples may be substituted by avalue.

In VVC, a video coder (e.g., video encoder 200 or video decoder 300, orin some examples, mode selection unit 202 of video encoder 200 orprediction processing unit 304 of video decoder 300) may be configuredto check the availability of reference samples by modifying thereference sample availability marking process (e.g., Clause 8.4.4.2.2)as shown below for PPRs with minimum samples of 16 chroma samples (64luma samples).

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to apply thedependent reference sample removal for the chroma components in bothsingle tree and dual tree. The video coder may be configured to restrictthe small chroma blocks in dual tree while the dependent removal may beapplied for the chroma components in single tree.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to apply thedependent removal for both the chroma component and luma component.

8.4.4.2.2 Reference Sample Availability Marking Process

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top left        sample of the current picture,    -   a variable refIdx specifying the intra prediction reference line        index,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   a variable cIdx specifying the colour component of the current        block,    -   a sample location (XR, YR) specifying the luma root location of        the PPR,    -   a variable curW specifying the width of the current transform        block,    -   a variable curH specifying the height of the current transform        block.

Outputs of this process are the reference samples refUnfilt[x][y] withx=−1−refIdx, y=−1−refIdx . . . refH−1 and x=−refIdx . . . refW−1,y=−1−refIdx for intra sample prediction.

The refW+refH+1+(2*refIdx) neighbouring samples refUnfilt[x][y] that areconstructed samples prior to the in-loop filter process, withx=−1−refIdx, y=−1−refIdx . . . refH−1 and x=−refIdx . . . refW−1,y=−1−refIdx, are derived as follows:

-   -   The neighbouring location (xNbCmp, yNbCmp) is specified by:        (xNbCmp,yNbCmp)=(xTbCmp+x,yTbCmp+y)   (8-108)    -   The current luma location (xTbY, yTbY) and the neighbouring luma        location (xNbY, yNbY) are derived as follows:        (xTbY,yTbY)=(cIdx==0)?(xTbCmp,yTbCmp):(xTbCmp<<1,yTbCmp<<1)  (8-109)        (xNbY,yNbY)=(cIdx==0)?(xNbCmp,yNbCmp):(xNbCmp<<1,yNbCmp<<1)  (8-110)    -   The distance (dXn, dYn) between current luma location (xTbY,        yTbY) and the luma root location of PPR are derived as follows:        dXn=xTbY−XR        dYn=yTbY−YR    -   An availability variable isRestricted specifying whether the        dependency among the current block and other blocks in the same        PPR occurred is derived as follows:        isRestricted=(dXn!=0∥dYn!=0)&&(curW*curH<16)&&cIdx!=0    -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighbouring blocks availability        checking process tbd] is invoked with the current luma location        (xCurr, yCurr) set equal to (xTbY, yTbY) and the neighbouring        luma location (xNbY, yNbY) as inputs, and the output is assigned        to availableN.    -   If isRestricted is equal to TRUE, availableN is updated as        follows:    -   If dXn !=0 && dYn !=0, availableN is set equal to FALSE,    -   If dXn !=0 && dYn==0, and x=−1−refIdx, y=0 . . . refH−1,        availableN is set equal to FALSE,    -   If dYn !=0 && dXn==0, and x=0 . . . refW−1, y=−1−refIdx,        availableN is set equal to FALSE.    -   Each sample refUnfilt[x][y] is derived as follows:    -   If availableN is equal to FALSE, the sample refUnfilt[x][y] is        marked as “not available for intra prediction”.    -   Otherwise, the sample refUnfilt[x][y] is marked as “available        for intra prediction” and the sample at the location (xNbCmp,        yNbCmp) is assigned to refUnfilt[x][y].

When a reference sample of a block in the PPR is not available, a videocoder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured tosubstitute this unavailable sample as follows.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to set theunavailable sample equal to a predefined value. This predefined valuemay be also based on the bit-depth being used to present the samples.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to set theunavailable sample equal to the average of the reconstructed samplesalong the border of the PPR.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to set thisunavailable sample equal to the value of the bottom-right sample of thetop-left neighbouring block. In the example, the top-left neighbouringblock and the current block share the same PPR and the video coder maybe configured to set this value equal to a predefined value that may bebased on the bit-depth being used to present the samples.

In case a PPR includes two separated blocks, a video coder (e.g., videoencoder 200 or video decoder 300, or in some examples, mode selectionunit 202 of video encoder 200 or prediction processing unit 304 of videodecoder 300) may be configured to process the blocks in this PPR beforeprocessing the intermediate blocks that do not belong to the region. Inthis example, if a prediction refers to a sample of the intermediateblock, the video coder may be configured to set the predicted valueequal to a predefined value.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to replacethe reference samples by the value of the bottom-right sample of thetop-left neighbouring block or the DC value when dXn and dYn arenon-zero.

A video coder (e.g., video encoder 200 or video decoder 300, or in someexamples, mode selection unit 202 of video encoder 200 or predictionprocessing unit 304 of video decoder 300) may be configured to fill thevalues of unavailable samples by the reference sample substitutionprocess defined in the specification, e.g., Clause 8.4.4.2.3 Referencesample substitution process of VVC WD4.

FIG. 13 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3 ), otherdevices may be configured to perform a method similar to that of FIG. 13.

Mode selection unit 202 initially predicts the current block (750). Forexample, mode selection unit 202 may form a prediction block for thecurrent block using intra prediction, inter prediction, or anothercoding mode. Mode selection unit 202 may partition video data using ablock size restriction. For example, mode selection unit 202 may apply ablock size restriction to prevent a splitting of a block that wouldresult in a small block comprising a block width and a block height whenthe block height times the block width is less than a threshold (e.g.,16). Residual generation unit 204 may then calculate a residual blockfor the current block (752). To calculate the residual block, residualgeneration unit 204 may calculate a difference between the original,uncoded block and the prediction block for the current block. Transformprocessing unit 206 and quantization unit 208 may transform and quantizecoefficients of the residual block (754). Entropy encoding unit 220 mayscan the quantized transform coefficients of the residual block (756).During the scan, or following the scan, entropy encoding unit 220 mayentropy encode the transform coefficients (758). For example, entropyencoding unit 220 may encode the transform coefficients using CAVLC orCABAC. Entropy encoding unit 220 may then output the entropy encodeddata of the block (760).

FIG. 14 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and 4), other devices may be configured to perform a method similar to thatof FIG. 14 .

Entropy decoding unit 302 may receive entropy encoded data for thecurrent block, such as entropy coded prediction information and entropycoded data for transform coefficients of a residual block correspondingto the current block (770). Entropy decoding unit 302 may entropy decodethe entropy encoded data to determine prediction information for thecurrent block and to reproduce transform coefficients of the residualblock (772). Prediction processing unit 304 may predict the currentblock (774), e.g., using an intra- or inter-prediction mode as indicatedby the prediction information for the current block, to calculate aprediction block for the current block. Prediction processing unit 304may determine a partitioning of video data using a block sizerestriction. For example, prediction processing unit 304 may apply ablock size restriction to determine a partition that prevents asplitting of a block that would result in a small block comprising ablock width and a block height when the block height times the blockwidth is less than a threshold (e.g., 16 samples). Entropy decoding unit302 may inverse scan the reproduced transform coefficients (776) tocreate a block of quantized transform coefficients. Inverse quantizationunit 306 and inverse transform processing unit 308 may inverse quantizeand inverse transform the coefficients to produce a residual block(778). Reconstruction unit 310 may ultimately decode the current blockby combining the prediction block and the residual block (780).

FIG. 15 is a flowchart illustrating an example method for encoding ablock using a block size restriction. Although described with respect tovideo encoder 200 (FIGS. 1 and 3 ), other devices may be configured toperform a method similar to that of FIG. 15 .

Mode selection unit 202 may partition video data into a plurality ofblocks using a block size restriction (802). For example, mode selectionunit 202 may apply a block size restriction to prevent a splitting of ablock of the plurality of blocks that would result in a small blockcomprising a block width and a block height when the block height timesthe block width is less than a threshold (e.g., 16). For instance, modeselection unit 202 may check various partitions and coding modes forrate-distortion only if the resulting partition satisfies the block sizerestriction (e.g., a splitting of a block of the plurality of blocksthat would not result in a small block comprising a block width and ablock height when the block height times the block width is less than athreshold). In some examples, mode selection unit 202 may apply theblock size restriction to prevent a splitting of only chroma componentsfor the block (and allow or permit a splitting of luma components forthe block). By preventing splits that lead to relatively small blocksizes, mode selection unit 202 may determine the prediction informationof blocks of a slice of video data with fewer block dependencies, thuspotentially decreasing coding complexity with little to no loss inprediction accuracy.

Mode selection unit 202 may generate prediction information for theblock (804). Mode selection unit 202 may generate a predicted blockbased on the prediction information (806). Residual generation unit 204may generate a residual block for the block based on differences betweenthe block and the predicted block (808). Entropy encoding unit 220 mayencode the residual block in the bitstream for the video data (810).

FIG. 16 is a flowchart illustrating an example method for decoding acurrent block of video data using a block size restriction. Althoughdescribed with respect to video decoder 300 (FIGS. 1 and 4 ), otherdevices may be configured to perform a method similar to that of FIG. 16.

Prediction processing unit 304 may determine a partition of video datainto a plurality of blocks using a block size restriction (852). Thepartition may apply a block size restriction to prevent a splitting of ablock of the plurality of blocks that would result in a small blockcomprising a block width and a block height when the block height timesthe block width is less than a threshold (e.g., 16). In some examples,the partition may apply the block size restriction to prevent asplitting of only chroma components for the block. By preventing splitsthat lead to relatively small block sizes, prediction processing unit304 may determine the prediction information of blocks of a slice ofvideo data with fewer block dependencies, thus potentially decreasingcoding complexity with little to no loss in prediction accuracy.

Prediction processing unit 304 may generate prediction information forthe block (854). Prediction processing unit 304 may generate a predictedblock based on the prediction information (856). Entropy decoding unit302 may decode a residual block for the block from the bitstream for thevideo data (858). Reconstruction unit 310 may combine the predictedblock and the residual block to decode the block (860).

A non-limiting illustrative list of examples of the disclosure aredescribed below.

Example 1: A method of processing video data, the method comprising:determining, by a video coder, a plurality of intra-coded blocks forgenerating prediction information; and processing, by a video coder, theplurality of intra-coded blocks in parallel to generate predictioninformation for a current block.

Example 2: The method of example 1, wherein determining the plurality ofintra-coded blocks comprises applying a block size restriction to theplurality of intra-coded blocks.

Example 3: The method of any combination of examples 1-2, furthercomprising: coding the one or more neighboring blocks of the intra-codedblocks without dependence between the one or more neighboring blocks.

Example 4: The method of example 3, wherein coding the one or moreneighboring blocks comprises selecting the one or more neighboringblocks based on a parallel-processable region.

Example 5: The method of any combination of examples 3-4, wherein codingthe one or more neighboring blocks comprises limiting the intraprediction mode candidate list of a block of the plurality ofintra-coded blocks based on a position of the block in the parallelregion.

Example 6: The method of any combination of examples 1-5, whereinprocessing the plurality of intra-coded blocks in parallel comprisesremoving a sample for the reference samples array that make neighboringblocks of the plurality of intra-coded blocks dependent.

Example 7: The method of any combination of examples 1-6, whereinprocessing the plurality of intra-coded blocks in parallel comprises:disabling IBC mode for small blocks.

Example 8: The method of any combination of examples 1-7, whereinprocessing the plurality of intra-coded blocks in parallel comprises:disabling IBC mode for small blocks excluding the first block in thePPR.

Example 9: The method of any combination of examples 7-8, wherein smallblocks comprises a block size of 2×2, 2×4, or 4×2.

Example 10: The method of any combination of claims 1-9, whereinprocessing the plurality of intra-coded blocks in parallel comprises:excluding all the blocks in a PPR from the IBC prediction area of otherblocks in the same PPR.

Example 11: The method of any combination of claims 1-10, whereinprocessing the plurality of intra-coded blocks in parallel comprises:setting the prediction samples for small IBC blocks in PPR equal to adefault value.

Example 12: The method of any combination of examples 1-12, whereinprocessing the plurality of intra-coded blocks in parallel comprises:determining the default value based on the bit-depth being used topresent the samples.

Example 13: The method of any combination of examples 1-13, whereinprocessing the plurality of intra-coded blocks in parallel comprises:clipping the motion vector of small chroma blocks in PPR such that thereference block should not overlap the PPR.

Example 14: A device for coding video data, the device comprising one ormore means for performing the method of any of examples 1-13.

Example 15: The device of example 14, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Example 16: The device of any of examples 14-15, further comprising amemory to store the video data.

Example 17: The device of any of examples 14-16, further comprising adisplay configured to display decoded video data.

Example 18: The device of any of examples 14-17, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Example 19: The device of any of examples 14-18, wherein the devicecomprises a video decoder.

Example 20: The device of any of examples 7-19, wherein the devicecomprises a video encoder.

Example 21: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of examples 1-13.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit.

Computer-readable media may include computer-readable storage media,which corresponds to a tangible medium such as data storage media, orcommunication media including any medium that facilitates transfer of acomputer program from one place to another, e.g., according to acommunication protocol. In this manner, computer-readable mediagenerally may correspond to (1) tangible computer-readable storage mediawhich is non-transitory or (2) a communication medium such as a signalor carrier wave. Data storage media may be any available media that canbe accessed by one or more computers or one or more processors toretrieve instructions, code and/or data structures for implementation ofthe techniques described in this disclosure. A computer program productmay include a computer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: determining, by one or more processors implemented incircuitry, according to a single tree partitioning scheme, a partitionof both a luma block associated with a block and a chroma blockassociated with the block, the single tree partitioning schemeindicating both a splitting of the luma block associated with the blockand a splitting of the chroma block associated with the block, whereinthe single tree partitioning scheme applies a block size restriction toprevent the splitting of the chroma block associated with the block thatwould result in a plurality of chroma blocks where each chroma block ofthe plurality of chroma blocks comprises a block width and a blockheight where the block height times the block width is less than athreshold; based on the block size restriction, determining, by the oneor more processors, not to split the chroma block according to thesingle tree partitioning scheme and splitting, by the one or moreprocessors, the luma block into a plurality of luma blocks according tothe single tree partitioning scheme; generating, by the one or moreprocessors, prediction information for the block based on the chromablock and the plurality of luma blocks; determining, by the one or moreprocessors, a predicted block for the block based on the predictioninformation; decoding, by the one or more processors, a residual blockfor the block; and combining, by the one or more processors, thepredicted block and the residual block to decode the block.
 2. Themethod of claim 1, wherein the threshold is
 16. 3. The method of claim1, wherein the chroma block comprises 16 samples.
 4. A method ofencoding video data, the method comprising: partitioning, by one or moreprocessors implemented in circuitry, according to a single treepartitioning scheme, both a luma block associated with a block and achroma block associated with the block, the single tree partitioningscheme indicating both a splitting of the luma block associated with theblock and a splitting of the chroma block associated with the block,wherein the partitioning comprises applying a block size restriction toprevent the splitting of the chroma block associated with the block thatwould result in a plurality of chroma blocks where each chroma block ofthe plurality of chroma blocks comprises a block width and a blockheight where the block height times the block width is less than athreshold; based on the block size restriction, determining, by the oneor more processors, not to split the chroma block according to thesingle tree partitioning scheme and splitting, by the one or moreprocessors, the luma block into a plurality of luma blocks according tothe single tree partitioning scheme; generating, by the one or moreprocessors, prediction information for the block based on the chromablock and the plurality of luma blocks; determining, by the one or moreprocessors, a predicted block for the block based on the predictioninformation; generating, by the one or more processors, a residual blockfor the block based on differences between the block and the predictedblock; and encoding, by the one or more processors, the residual block.5. The method of claim 4, wherein the threshold is
 16. 6. The method ofclaim 4, wherein the chroma block comprises 16 samples.
 7. A device fordecoding video data, the device comprising: a memory configured to storevideo data; and one or more processors implemented in circuitry andconfigured to: determine, according to a single tree partitioningscheme, a partition of both a luma block associated with a block and achroma block associated with the block, the single tree partitioningscheme indicating both a splitting of the luma block associated with theblock and a splitting of the chroma block associated with the block,wherein the single tree partitioning scheme applies a block sizerestriction to prevent the splitting of the chroma block associated withthe block that would result in a plurality of chroma blocks where eachchroma block of the plurality of chroma blocks comprises a block widthand a block height where the block height times the block width is lessthan a threshold; based on the block size restriction, determine not tosplit the chroma block according to the single tree partitioning schemeand split the luma block into a plurality of luma blocks according tothe single tree partitioning scheme; generate prediction information forthe block based on the chroma block and the plurality of luma blocks;determine a predicted block for the block based on the predictioninformation; decode a residual block for the block; and combine thepredicted block and the residual block to decode the block.
 8. Thedevice of claim 7, wherein the threshold is
 16. 9. The device of claim7, wherein the chroma block comprises 16 samples.
 10. A device forencoding video data, the device comprising: a memory configured to storevideo data; and one or more processors implemented in circuitry andconfigured to: partition, according to a single tree partitioningscheme, both a luma block associated with a block and a chroma blockassociated with the block, the single tree partitioning schemeindicating both a splitting of the luma block associated with the blockand a splitting of the chroma block associated with the block, wherein,to partition, the one or more processors are configured to apply a blocksize restriction to prevent the splitting of the chroma block associatedwith the block that would result in a plurality of chroma blocks whereeach chroma block of the plurality of chroma blocks comprises a blockwidth and a block height where the block height times the block width isless than a threshold; based on the block size restriction, determinenot to split the chroma block according to the single tree partitioningscheme and split the luma block into a plurality of luma blocksaccording to the single tree partitioning scheme; generate predictioninformation for the block based on the chroma block and the plurality ofluma blocks; determine a predicted block for the block based on theprediction information; generate a residual block for the block based ondifferences between the block and the predicted block; and encode theresidual block.
 11. The device of claim 10, wherein the threshold is 16.12. The device of claim 10, wherein the chroma block comprises 16samples.